Method for the closed-loop control of the regeneration of a particle filter

ABSTRACT

The invention concerns a method for the closed-loop control of the regeneration of a particle filter in the exhaust gas system of an internal combustion engine, wherein the burn-off of particles in the particle filter during a regeneration process is controlled by a closed-loop control of the oxygen content of the exhaust gas and/or wherein the temperature of the exhaust gas or of at least one component of the exhaust gas aftertreatment system is controlled in a closed loop. Provision is thereby made for the corrective controller actions for the closed-loop control of the oxygen content and/or the temperature of components of the exhaust gas aftertreatment system to take place only during stable combustion conditions of the internal combustion engine. 
     The method prevents through corrective controller actions during insufficiently stable combustion conditions of the internal combustion engine conditions in the exhaust gas aftertreatment system of the internal combustion engine from being produced, which lead to an inadmissibly high temperature of individual components of the exhaust gas aftertreatment system.

TECHNICAL FIELD

The invention concerns a method for the closed-loop control of the regeneration of a particle filter in the exhaust gas system of an internal combustion engine, wherein the burn-off of particles in the particle filter is controlled during a regeneration process by means of a closed-loop control of the oxygen content of the exhaust gas and/or wherein the temperature of the exhaust gas or of at least one component of an exhaust gas after-treatment system is controlled in a closed loop.

BACKGROUND

In the text of the German patent DE 103 33 441 A1, a method for the open-loop control of an exhaust gas aftertreatment system, especially a particle filter, of an internal combustion engine is described, wherein a nominal value (LAS) for a lambda signal (L) or a change in a lambda signal (L) is specifiable and an actual value for the lambda signal (L) is acquired; and wherein, based on the comparison between the actual value and the nominal value, a gating signal for an actuator, with which the reaction in the exhaust gas after-treatment system can be controlled in an open loop, is specified in such a way that the actual value approaches the nominal value.

In so doing, the nominal value (LAS) can be specified in such a way that a specified burn-off speed of the particles of a particle filter contained in the exhaust gas after-treatment system is reached and/or that a specified temperature of the exhaust gas after-treatment system is reached.

By means of this kind of a closed-loop controlled, oxygen restricted regeneration operation of the particle filter, the burn-off rate of the soot particles and consequently the temperature increase in the particle filter, which is caused by the exothermal progression of the reaction, can be effectively controlled. A limitation of the maximum temperatures occurring during a regeneration phase is particularly necessary if in comparison to standard materials, such as carbon silicide, more cost effective materials, such as cordierite, are resorted to in production. This results from the fact that these materials have a smaller thermal load capacity. Therefore, when such cost effective materials are involved during the regeneration, the temperature of the particle filter may not exceed a maximum value of approximately 850° C. to 1000° C.

In the text of the German patent DE 103 33 441 A1, a device for the open-loop control of an exhaust gas after-treatment system, especially a particle filter, of an internal combustion engine is additionally described with wherewithal, which specifies a nominal value (LAS) for a lambda signal (L) or a change in a lambda signal (L), with wherewithal, which acquires an actual value for the lambda signal (L) or for a change in the lambda signal (L), and with wherewithal, which based on the comparison between the actual value and the nominal value (LAS) of the lambda signal (L) or on the change in the lambda signal (L), specifies a gating signal for an actuator, with which the reaction in the exhaust gas after-treatment system can be controlled in an open loop in such a way that the actual value approaches the nominal value. In so doing, the quantity of oxygen in the exhaust gas can be influenced by means of the actuator. The actuator can be embodied as an exhaust gas recirculation valve, a throttle valve or embodied to influence an exhaust gas turbo charger; or it can be a fuel metering system, which at least performs an afterinjection into the internal combustion engine.

The effectiveness of the control unit interventions greatly depends on the operating conditions of the internal combustion engine. Hence, measures in the fuel injection system to control, for example, lambda, for example in the form of an afterinjection, which is burnt neutral in terms of the engine torque, must have a defined combustion in the internal combustion engine. Otherwise an inadmissible reaction taking place exothermally in the exhaust gas aftertreatment system, particularly in an oxidizing catalytic converter, can arise on account of the increased emissions of uncombusted hydrocarbons. Said reaction can lead to a marked increase in temperature; and thereby in the aforementioned example damage to the oxidizing catalytic converter can result.

It is the task of the invention to provide a method, wherein inadmissible increases in temperature in the exhaust gas aftertreatment system of an internal combustion engine, which are caused by corrective controller actions to control the burn-off of soot particles in an open loop during the regeneration of particle filters, can be avoided with certainty.

SUMMARY

The task is thereby solved, in that corrective controller actions to control the oxygen content in the exhaust gas in a closed loop and/or the temperature of components of the exhaust gas aftertreatment system take place only when stable combustion conditions of the internal combustion engine exist. During such stable combustion conditions, the corrective controller action does not lead, for example, to an inadmissibly high emission of uncombusted hydrocarbons. In so doing, an exothermal reaction, which proceeds too powerfully in the exhaust gas aftertreatment system of the internal combustion engine, especially in an oxidation catalytic converter, is not brought about by the corrective controller action. Furthermore, a large emission of hydrocarbons, which causes a distortion of the lambda measurement in the exhaust gas duct due to cross sensitivities of the lambda probe to hydrocarbons, can be avoided with certainty. The closed-loop control of the oxygen content during the regeneration phase of the particle filter takes place on the basis of the measured lambda signal. A large concentration of uncombusted hydrocarbons in the exhaust gas leads to a distortion of the measured lambda signal toward lean exhaust gas compositions, which in turn causes a corrective controller action to reduce the oxygen content in the exhaust gas, whereby the concentration of uncombusted hydrocarbons in the exhaust gas is still further increased. This can be avoided with certainty with implementation of the method according to the invention.

Inadmissible corrective controller actions during insufficiently stable combustion conditions can thereby be avoided with certainty, in that the regeneration process of the particle filter takes place only during stable combustion conditions of the internal combustion engine.

In so doing, provision can particularly be made in the case of a cold internal combustion engine for the on-position of the glow plug system to be used to establish the state of stable combustion conditions of the internal combustion engine. As measurements on internal combustion engines have confirmed, a sufficiently stable combustion for a corrective controller action can also be brought about in very cold internal combustion engines at −20° C. if the glow heating phase is turned on. On the other hand, the engine combustion breaks down when the glow heating phase is turned off, whereby the concentration of uncombusted hydrocarbons in the exhaust gas increases with the effects on the closed-loop lambda control, which have already been described. Corrective controller actions in a cold internal combustion engine should thus be restricted to the on-position of the glow heating phase.

Provision can be made according to a preferred variation of embodiment of the invention for the stability of the rotational speed of the internal combustion engine to be used to detect stable combustion conditions of the internal combustion engine. The stability of the engine rotational speed allows for the direct acquisition of the stability of the combustion of the internal combustion engine. If the shapelessness of the engine rotational speed exceeds a specified threshold value, a stability of combustion is suggested, which is insufficient for exhaust gas aftertreatment corrective actions. At the same time the engine rotational speed is generally already made available to an overriding open-loop control of the internal combustion engine.

The method particularly allows itself to be advantageously employed for the closed-loop control of the regeneration of particle filters with a body material of cordierite. The manufacturing costs of particle filters can be significantly reduced through the utilization of cordierite as the particle filter material. This requires the exact maintenance of the maximum temperature load on the particle filter and in so doing the employment of lambda and temperature controllers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below in detail using the examples of embodiment depicted in the figures. The following are shown:

FIG. 1 in schematic depiction the technical environment, in which the invention can be employed,

FIG. 2 a first diagram of the combustion stability as a function of the glow heating phase,

FIG. 3 a second diagram with a pattern of a lambda signal as a function of the glow heating phase,

FIG. 4 a third diagram with a time history of a lambda controller quantity as a function of the glow heating phase,

FIG. 5 a fourth diagram with a temperature curve of an oxidation catalytic converter as a function of a corrective controller action.

DETAILED DESCRIPTION

FIG. 1 shows in schematic depiction the technical environment, wherein the invention can be employed. An internal combustion engine 10 is depicted in the form of a diesel engine with a fuel-delivery control system 11, an air intake manifold 20, in which a supply air stream 21 is carried, and an exhaust gas duct 30, in which an exhaust gas stream 32 of the internal combustion engine 10 is carried. A compression stage 23 of a turbocharger 22 and a throttle valve 24 are disposed along the air intake manifold 20 in the direction of flow of the supply air stream 21. An exhaust gas recirculation 25 connects the air intake manifold 20 with the exhaust gas duct 30 via an exhaust gas recirculation valve 26. After the internal combustion engine 10 in the direction of flow of the exhaust gas stream 32, an exhaust gas turbine 31 of the turbocharger 22 is depicted as well as a first lambda probe 43, a fuel delivery 45, an oxidation catalytic converter 41 in the form of a diesel oxidation catalytic converter, a second lambda probe 44, as well as a particle filter 42 in the form of a diesel particle filter as component parts of an exhaust gas aftertreatment system 40. At least one of the two lambda probes 43, 44 is required to implement the invention.

Fresh air is supplied to the internal combustion engine 10 via the air intake manifold 20. In the process, the fresh air is compressed by the compression stage 23 of the turbocharger 22. The compression stage 23 is driven by the exhaust gas stream 32 via the exhaust gas turbine 31. The air quantity supplied can be adjusted by the throttle valve 24. In order to reduce toxic emissions, exhaust gas from the exhaust gas duct 30 is admixed with the supply air stream 21 by way of the exhaust gas recirculation 25 in quantities dependent on the operating parameters of the internal combustion engine 10. The exhaust gas recirculation rate can at the same time be adjusted with the aid of the exhaust gas recirculation valve 26.

Toxic emissions emitted by the internal combustion engine 10 are converted, respectively filtered out, in the exhaust gas aftertreatment system 40. Thus, hydrocarbons are oxidized in the oxidation catalytic converter 41, while soot particles are retained in the particle filter 42.

Fuel can be introduced into the exhaust gas duct 30 via the fuel delivery 45.

Open-loop and closed-loop control units, which are necessary for the operation of the internal combustion engine 10 and the exhaust gas aftertreatment system 40, temperature sensors as well as units to diagnose the depletion of the particle filter 42 are not depicted.

The particle filter 42 fills up as a result of the operation of the internal combustion engine 10 until the achievement of its storage capacity is signaled. A regeneration phase of the particle filter 42 is thereupon initiated, in which the particles stored in the particle filter 42 are burned up in a reaction progressing exothermally. In order to initiate this exothermic reaction, exhaust gas temperatures from 600° C. to 650° C. are necessary before the particle filter 42. Because these temperatures during normal operation of the internal combustion engine 10 are only achieved near full load, an increase in temperature has to be brought about by additional measures. Beside air system corrective actions, for example by way of the throttle valve 24, additional measures in the environment of the fuel injection via the fuel-delivery control system 11 are required especially in the case of low engine loads and low engine rotational speeds. These can be measures within the engine itself like a retardation of the main fuel injection or an afterinjection PoI2, which is burnt neutral in terms of torque in the internal combustion engine 10, or an afterinjection PoI1, which is fed via the fuel delivery 45 into the exhaust gas duct 30 before the oxidation catalytic converter 41 and is burnt at the oxidation catalytic converter 41. Furthermore, a change in the exhaust gas recirculation rate is possible by way of the exhaust gas recirculation valve 26.

The aforementioned measures also influence the composition of the exhaust gas beside the exhaust gas temperature, particularly its oxygen content. Because the oxygen content has a significant influence on the burn-off speed of the particles stored in the particle filter 42 during the regeneration process and in so doing on the energy thereby released for every unit of time, it is known how to control in a closed loop the progression of the particle burn-off and thereby the temperature of the particle filter via a closed-loop control of the oxygen content of the exhaust gas using the aforementioned measures. For this purpose, the signal or the signal change of at least one of the two lambda probes 43, 44 is compared with a set point value in a control unit, which is not depicted; and on the basis of the offset obtained, a measure or a combination of several of the aforementioned measures is taken.

The maximum temperature of the particle filter 42 can be restricted by the closed-loop control of the temperature of the particle filter 42 via the oxygen content of the exhaust gas. This makes it possible for materials having a lower thermal load capacity, as for example cordierite, which are cost effective in comparison with standard materials such as carbon silicide, to be employed.

The signals depicted in FIGS. 2 to 5 exemplary refer to the technical environment depicted in FIG. 1. The identifiers are correspondingly carried over.

FIG. 2 shows in a first diagram 50 the combustion stability of an internal combustion engine, for example of the internal combustion engine 10 depicted in FIG. 1, as a function of the glow heating phase as a possible indicator for a stable combustion at low ambient temperatures, in this case at −20° C. In so doing, while referring to a first time axis 51, the progression of an engine rotational speed 57, which is plotted against a first ordinate 52 of the diagram 50, and the progression of an injected fuel quantity 58 intended for each fuel injection, which is plotted against a second ordinate 53, are depicted. The diagram 50 is divided into a first time interval 55 and a second time interval 56, separated at a switching point 54. During the first time interval 55, the glow heating phase of the internal combustion engine 10 is switched on and during the second time interval 56 switched off.

The diagram 50 shows how the rotational speed 57 of the internal combustion engine 10 changes as a function of the switching status of the glow heating phase when the injected fuel quantity 58 remains constant and how correspondingly the engine's combustion breaks down by switching off the glow heating phase. The hydrocarbon content in the exhaust gas of the internal combustion engine 10 increases as a result.

FIG. 3 shows in a second diagram 60 a time history of a measured lambda signal 63, which refers to a third ordinate 62, in the exhaust gas of the internal combustion engine 10 as a function of the switching status of the glow heating phase depicted in FIG. 2. Said time history is also shown plotted against a second time axis 61 with the same subdivisions as the first time axis 51 depicted in FIG. 2. The switching point 54 from FIG. 2 is correspondingly carried forward. The lambda measurement can be carried out with one of the lambda probes 43, 44 depicted in FIG. 1.

The measurement of the lambda signal 63 was carried out at the switching point 54, where the lambda remains steady. The increase in the measured lambda signal 63 can be traced back to the known cross sensitivities of the lambda probe 43, 44 to the increased proportion of hydrocarbons in the exhaust gas after the switching point 54. Said increase is thus based on an erroneous measurement of the lambda probe 43, 44.

In a third diagram 70 in FIG. 4, a time history of a lambda control quantity of an afterinjection 73, which is burnt neutral in terms of torque, is depicted as a function of the glow heating phase within a closed loop, which has already been described, for the controlled burn-off of particles during the regeneration of a particle filter 42. Said time history is also in this case plotted against a third time axis 71 with the same subdivisions as in the first time axis 51 depicted in FIG. 2 and with a switching point 54, which has correspondingly been carried forward, whereby the quantity of fuel of the early afterinjection 73 is plotted on a fourth ordinate 72.

The early afterinjection 73 is mentioned in the example of embodiment as a substitution for the measures to control the oxygen content in the exhaust gas of the internal combustion engine 10 in a closed loop in order to control the burn-off speed of particles during the regeneration phase of the particle filter 42 in a closed loop.

The increase in the injected fuel quantity after the switching point 54 results on the basis of the lambda signal 63 depicted in FIG. 3, which was erroneously determined.

FIG. 5 shows a fourth diagram 80 with a temperature curve 83 of an oxidation catalytic converter 41 as a function of a corrective controller action to control the burn-off speed of particles during the regeneration phase of the particle filter 42. In so doing, the temperature is plotted on a fifth ordinate 82 against a fourth time axis 81. The time axis 81 comprises an extended time interval in comparison to the times axes 51, 61, 71 depicted in the FIGS. 2, 3, 4. The switching point 54 between the on-position of the glow heating phase and the off-position of the glow heating phase is correspondingly carried forward.

The proportion of uncombusted hydrocarbons in the exhaust gas of the internal combustion engine before the oxidation catalytic converter 41 increases due to the lambda signal 63 depicted in FIG. 3, which was erroneously determined, and the increase in the early afterinjection 73 depicted in FIG. 4, which was initiated as a result of said signal. A substantial exothermic reaction thus results in the oxidation catalytic converter 41, whereby its temperature rises to 1000° C. in the depicted example of embodiment.

The oxidation catalytic converter 41 can be damaged as a result of this substantial temperature increase in the oxidation catalytic converter 41, which is induced by an erroneous corrective action by the closed-loop system to control the burn-off speed of particles in the particle filter 42 during the regeneration process. The erroneous corrective action of the closed-loop system is thereby based on an erroneous measurement of the lambda probe 43, 44, which in turn can be traced back to an insufficient stability in the combustion of the internal combustion engine 10.

Provision is consequently made according to the invention for corrective controller actions or the regeneration of the particle filter to generally be limited to operating phases of the internal combustion engine 10 with stable engine combustion conditions. When the internal combustion engine 10 is cold, the switching status of the glow plug system can be used as a possibility to indirectly detect a stable combustion. Hence, a corrective controller action or the regeneration of the particle filter 42 can be limited to time intervals 55, in which the glow heating phase is turned on. Another possibility exists in the direct acquisition of the combustion stability through the evaluation of the shapelessness of the engine rotational speed signal. If this shapelessness of the engine rotational speed exceeds a certain threshold, an insufficient combustion stability is suggested for exhaust gas aftertreatment corrective actions. 

1. A method of regenerating a particle filter in an exhaust gas system of an internal combustion engine, the method comprising: controlling a burn-off of particles in the particle filter by a closed-loop control of the exhaust gas oxygen content; controlling a temperature of the exhaust gas or a temperature at least one component of an exhaust gas aftertreatment system; and if stable combustion conditions of the internal combustion engine exist, providing corrective controller actions to control the oxygen content in a closed loop or to control the temperature of the exhaust gas aftertreatment system.
 2. A method according to claim 1, wherein a regeneration process of the particle filter only takes place at stable combustion conditions of the internal combustion engine.
 3. A method according to claim 1, further comprising establishing a state of stable combustion conditions of the internal combustion engine by switching a status of a glow plug system.
 4. A method according to claim 1, further comprising using a stability of a rotational speed of the internal combustion engine to detect stable combustions conditions of the internal combustion engine.
 5. A method according to claim 1, wherein a body material of the particle filter is cordierite. 